Production of water-less lithographic plates

ABSTRACT

There is described a method of preparing a water-less lithographic plate by coating a positive working photosensitive composition onto an oleophilic base imagewise exposing the plate and developing it to remove the areas of the photosensitive composition which have been light exposed, coating overall the surface of the plate with a layer of a composition which is ink-releasing or when cured becomes ink releasing, then either as a separate step or as a combined step curing the ink-releasing composition or drying the ink-releasing composition and light exposing overall the plate, then redeveloping the plate to remove the photosensitive composition remaining after the first development and any ink-releasing composition overlying the photosensitive composition.

This invention relates to the production of so-called water-lesslithographic plates.

Lithographic plates may be divided into two classes. Those which requiredampening water which is fed to the non-image areas of the plate, formsa water film and acts as an ink-repellant layer; this is the so-calledfount solution and those which require no fount solution are calleddriographs or water-less lithographic plates. Most lithographic platesat present in use are of the first type and require a fount-solutionduring printing. However, lithographic plates of this type suffer from anumber of disadvantages. Some of these are:

a) adjustment of the proper ink-water balance during press operation isdifficult and requires great experience. If the correct ink-waterbalance is not achieved scumming is occasioned when the printed inkimage extends into the non-image areas ruining the printed image.

b) adjustment of the ink-water balance at start-up or re-start up isparticularly difficult and can not be stabilised until a large number ofsheets have been printed, thus incurring waste,

c) the ink tends to become emulsified which leads to poor adherence ofthe ink on to the plate which causes problems in colour reproduction andin dot reproduction,

d) the printing press has to be provided with a dampening system, thusincreasing its size and complexity.

e) The plate care chemistry and fount solutions require careful controland selection. Further plate cleaners contain significant levels ofsolvent which is not desirable.

However, with water-less plates in which the ink-releasing layer is, forexample, a cured silicone layer there is no scumming and clearer imagescan be produced. Very often water-less plates comprise a base material,for example aluminium plate, on which a photosensitive layer is coated,on this photosensitive layer there is coated a silicone layer. Afterimagewise exposure and development in which selected areas of thephotosensitive composition are altered, the overlying silicone layer isremoved and the plate is inked up. The ink adheres only to those areasof the plate not covered by the silicone remaining after development.Thus the plate can be printed without the need to use a fount solution.

However, in practice it has proved difficult to get the silicone layercomposition to adhere to the photosensitive layer. In spite of the ideaof water-less plates having been described in patent specifications forat least fifteen years very little has been done to commercialise theidea and water-less plates which have been and are being sold are moreexpensive than the conventional plates which require a fount solution.

It is the object of the present invention to provide a novel method ofpreparing a water-less lithographic plate.

Therefore, according to the present invention there is provided a methodof preparing a water-less lithographic plate by coating a positiveworking photosensitive composition onto an oleophilic base, imagewiseexposing the plate and developing it to remove the areas of thephotosensitive composition which have been light exposed, coatingoverall the surface of the plate with a layer of a composition which isink releasing, or when cured becomes ink releasing, then either as aseparate step or as a combined step, curing the ink releasingcomposition or drying the ink releasing composition and light exposingoverall the plate, then redeveloping the plate to remove thephotosensitive composition remaining after the first development and theink releasing composition which overlaid it.

In order to minimise the possibility of the ink releasing substanceremaining on the positive working composition after the redevelopmentstep an additional step between first developing step and coatingoverall the plate with the ink-releasing substance may be employed,which comprises treating the plate with an oleophilic coatingcomposition which adheres to the remaining positive working compositionbut which does not adhere to the exposed base to form a thin opticallylight transparent coating on the remaining positive working composition.The ink-releasing substance does not adhere to this thin coating.

Suitable oleophilic substances to use are esters based on coconut fattyacid. Such substances are wiped on the plate after the first developingstep to provide a very thin layer.

In one method of the present invention the ink-releasing composition iscured in a separate step. For example the ink-releasing composition maybe heat curable.

In an alternative method of the present invention the ink-releasingcomposition is U.V. light curable. Thus in this method a single steponly is required to cure the ink-releasing composition and to overallexpose the plate.

In another method of the present invention the ink-releasing compositionis initially ink-releasing but requires to be dried.

The method of the present invention yields a positive working water-lesslithographic plate in which the ink releasing composition remaining onthe plate constitutes the oleophobic or ink releasing areas of theplate, whilst the areas of the plate from which the photosensitivecomposition was removed by the second development step constitutes theoleophilic areas of the plate.

After the second development step and drying, the plate can be inked up.The ink is held in the areas between the portions of ink releasingcomposition which remain on the plate. No fount solution is required todifferentiate between the oleophilic and the ink releasing areas of theplate when printing using an oleophilic printing ink.

The oleophilic base used in the method of the present invention ispreferably an aluminium plate which will carry on its surface a thinaluminium oxide layer due to action with atmospheric oxygen. This layermay be of increased thickness due to anodising treatment of the base.Post anodic treatment of the base to increase its oleophilicity may beundertaken. This treatment following electrochemical graining provides aconventional litho base which may be used in the method of the presentinvention.

Alternatively the aluminum base may be an ungrained base which has beenanodised and then optionally silicated. For example the following methodmay be used.

A solution of 3% sodium silicate was made up in deionised water. Thiswas heated to a temperature of 50° C. in a waterbath. The anodised onlysubstrate was immersed for 30 seconds before being washed thoroughly andplaced into an 80° C. oven for 5 minutes.

A particularly useful base is obtained when the ungrained but anodisedaluminium base is silicated as above and then coated with for exampleδ-aminopropyltrimethoxysilane.

A particularly useful coating solution is a 1:990 solution ofδ-aminopropyltrimethoxysilane in n-heptane.

Alternatively or in addition the aluminium base may have been coatedwith a layer which gives the coated base improved oleophilicity over theuncoated base. Examples of such coatings are a negative workingphotosensitive composition or an oleophilic polymer for example ethylcellulose or a resol type resin.

The coating over the aluminium base plate whether treated or not may becoated with a so-called primer layer as described for example in E.P.44220, U.S. Pat. No. 5,061,598 and E.P. 560347. Such primer layers maycomprise a large variety of polymers such as polyester, polyurethanesand polyamides and help to provide a better printing surface than isafforded by uncoated aluminium.

Another base material which may be used in the method of the presentinvention is a plastics material base or a treated paper base as used asbase in the photographic industry. A particularly useful plasticsmaterial base is polyethylene terephthalate which has been subbed torender its surface oleophilic. A so-called resin coated paper which hasbeen corona discharge treated may also be used.

Preferably the ink releasing composition is a silicone based polymer.

Other substances which can be used instead of silicone based polymers inthe ink-releasing composition include fluoro-alkyl compounds asdescribed in U.S. Pat. No. 3,910,187, U.S. Pat. No. 4,424,325, U.S. Pat.No. 4,087,584 and U.S. Pat. No. 4,724,195.

Examples of useful silicone polymers are organo functional siloxanes.One such siloxane is available from Dow Corning as a 40% solids emulsionunder the designation SYL OFF 7920.

Usefully a curing catalyst may be used in conjunction with theink-releasing composition. For example a platinum based catalystmarketed by Dow Corning under the designation SYL OFF 7922 may be usedto cure SYL OFF 7920.

A useful siloxane coating composition for use of the method of thepresent invention comprises:

4 parts by weight of SYL OFF 7920

1 part by weight of SYL OFF 7922

2 parts by freight of water

This is hereinafter referred to as siloxane coating composition A.

Another useful silicone for use as release agent which is coated as anorganic solvent based formulation comprises 0.375 g (viscosity 500 ctsk)polydimethyl siloxane vinyl dimethyl terminated, 0.105 gmethylhydrodimethyl siloxane co-polymer +1 drop of platinum divinyltetramethyl disiloxane (catalyst) in 1.53 g of isopar G: toluene.(14:2.5) ratio.

Preferably the ink-releasing composition comprises a proportion of awater soluble polymer for example polyvinyl alcohol or a cellulose ethersuch as hydroxy propyl cellulose.

A modified siloxane composition for use in the present inventioncomprises:

4 parts by weight of SYL OFF 7920

1 part by weight of SYL OFF 7922

2 parts by weight of aqueous solution which comprise 10% by weight ofpolyvinyl alcohol of (Gohsenol NM 14)

This siloxane composition is hereafter referred to as siloxane coatingcomposition B.

When the ink-releasing coating composition comprises a catalyst such asSYL OFF 7922 which contains platinum the composition is heat-curable attemperatures over 100° C. Thus when such an ink-releasing coatingcomposition is used a separate ink-releasing composition curing step isrequired. Examples of other platinum based catalysts are described inE.P. 560347.

Usefully the ink-releasing composition curing catalyst may be presentcoated on or in the oleophilic base. Thus curing of the compositiontakes place preferentially in those areas of the plate from which thephotosensitive composition has been removed after the first developingstep.

Other ink-releasing coating compositions are curable by U.V. exposure ifthey comprise an initiator which is activated by U.V. Such initiatorsare described in U.S. Pat. No. 3,865,588, and include aromatic ketones,hexaarylbiimidazoles and pyrilium salts.

Such initiators may also be present coated on or in the oleophilic base.

An example of a fluoro-alkyl compound composition which is U.V. curablecomprises

    ______________________________________                                        Zonyl TM          1          g                                                  Zonyl TA-N 2 g                                                                Irgacure 907 0.1 g                                                            Methyl Ethyl Ketone 2 g                                                     ______________________________________                                    

This fluoro-alkyl compound composition is hereinafter referred to asfluoroalkyl coating composition C. The Zonyl products are marketed by DuPont, the Irgacure is marketed by Ciba-Geigy.

An example of a fluoro compound composition which is initiallyink-releasing but in use requires to be air dried at about 100° C. is a17% by weight of ZONYL 8070 dispersed in water. ZONYL is a fluoro alkylpolymer marketed by Du Pont.

This is hereinafter referred to as fluoroalkyl coating composition D.

Usefully a curing inhibitor may be present in the positive layer. Thisreduces the amount of ink-releasing composition which adheres to thepositive photosensitive composition areas which are left after the firstdevelopment and exposure. This aids in the complete removal of suchpositive areas after the second exposure and development. An example ofa suitable curing inhibitor is hydroquinone.

In order to reduce the amount of ink releasing composition which sticksto the positive photosensitive composition left after the firstdevelopment the binder for this photosensitive composition may compriseat least one cellulosic compound such as ethyl cellulose.

Depending on the optical sensitivity of the photosensitive compositionthe imagewise exposure may be a contact exposure, a projection exposureor an exposure in an image setter to an electromagnetic radiation orheat source, typically a scanning laser.

Preferably the positive working photosensitive composition comprises an0-quinone diazide compound.

Examples of particularly preferred o-quinone diazide compounds aredisclosed in a variety of publications such as U.S. Pat. Nos. 2,766,118;2,767,092; 2,772,972; 2,859,112; 2,907,665; 3,046,110; 3,046,111;3,046,115; 3,046,118; 3,046,119; 3,046,120; 3,046,121; 3,046,122;3,046,123; 3,061,430; 3,102,809; 3,106,465; 3,635,709 and 3,647,443 andthese compounds may preferably be used in the invention. Among these,particularly preferred are o-naphthoquinonediazidosulfonates oro-naphthoquinonediazidocarboxylates of aromatic hydroxyl compounds;o-naphthoquinonediazidosulfonic acid amides or o-naphthoquinonediazido-carboxylic acid amides of aromatic amine compounds, for instance, estersof benzoquinone-1, 2-diazidosulfonic acid or naphthoquinone-1,2-diazidosulfonic acid with polyhydroxyphenyl (hereinafter the term"ester" also include partial esters); esters of naphthoquinone-1,2-diazido-4-sulfonic acid or naphthoquinone-1,2-diazido-5-sulfonic acidwith pyrogallol/acetone resins; esters of benzoquinone-1,2-diazidosulfonic acid or naphthoquinone-1,2-diazidosulfonic acid withnovolak type phenol/formaldehyde resins or novalak typecresol/formaldehyde resins; amides of poly(p-aminostyrene) andnaphthoquinone-1, 2-diazido-4-sulfonic acid ornaphthoquinone-1,2-diazido-5-sulfonic acid; esters ofpoly(p-hydroxystyrene) and naphthoquinone-1,2- diazido-5-sulfonic acid;esters of polyethylene glycol with naphthoquinone-1,2-diazido-4-sulfonic acid or naphthoquinone-1, 2-diazido 5-sulfonicacid: amides of polymeric amines with naphthoquinone-1,2-diazido-4-sulfonic.

A particularly useful positive working composition comprises atriarylmethane dye, a triazine acid generator, 2,4 Naphthaquinonediazide sulphonic acid ester of a phenol resin.

This is hereinafter referred to as positive working photosensitivecomposition A.

An example of a developing solution used in both the first developmentstep and second development step in the process of the present inventionthat is to say to remove the exposed positive photosensitive areas ofthe photosensitive composition after the first exposure are and afterthe second exposure is an aqueous solution of 8% metasilicate, 0.1% ofan organic phosphite ester of an ethoxylated alcohol and 0.01% ofpolyoxy propylene methyl ethyl ammonium chloride. This is hereinafterreferred to as Developing solution A.

In order to illustrate the various steps of the process of the presentinvention reference is made to the accompanying drawings.

FIGS. 1A-C, 2A-C, 3A-E, 4A-C and 5A-C show the steps in the preparationof a water-less lithographic plate from a presensitised lithographicplate.

In FIG. 1A the starting plate comprises the positive workingphotosensitive composition A or an aluminium plate.

In FIG. 1A there is coated on the grained oleophilic aluminium plate 1the positive working photosensitive composition 2. Shown above the plateis a mask 3.

This plate is treated by the following steps, exposure through the mask3, then developed in developing solution A. This development stepremoves the light exposed areas of the photosensitive composition 2. Thedeveloped plate is then coated overall wits siloxane coating compositionA.

The siloxane coating is then heat cured at 110° C. for one minute.

This yields the plate as shown in FIG. 1B, wherein 1 is the aluminiumplate, 2 shows the photosensitive composition remaining afterdevelopment and 5 shows the cured siloxane both on the remainingphotosensitive composition 2 and directly coated on the plate 5a. Theplate shown in 1B is then subjected to an overall visible light exposureand is then redeveloped in developing solution A. The resulting plate isas shown in FIG. 1C.

The grained oleophilic aluminium plate 1 has areas of 1b with no coatingthereon. On areas 1c it is coated with the cured siloxane coating 5.

The plate shown in FIG. 1C can be inked up with an oleophilic ink whichadheres to areas 1b of the aluminium plate but not to areas Ic which iscoated with the cured siloxane 5. This inked up plate can be used as awater-less printing plate requiring no. fount solution.

In a small modification to the method described with reference to theplate of FIG. 1A. After the first development step the plate 1 wascoated overall with silicone coated composition B which comprises asmall proportion of polyvinyl alcohol. This has the effect of making iteasier to remove the siloxane coating 5 on the remaining photosensitivecomposition 2 in figure B but the siloxane in FIG. 1C was not affected.

In FIG. 2A the plate comprising the same aluminium plate as used in FIG.1 was coated with the same positive working coating composition 2 asused in FIG. 1.

The plate of FIG. 2B was then exposed through mask 3, developed indeveloping solution A to remove the light exposed areas of thephotosensitive composition 2. The developed plate was then coatedoverall with the fluoro coating composition C which is U.V. lightcurable.

The plate was overall U.V. light exposed. This cures the fluoro coatingcomposition and exposes the remaining photosensitive composition. Theplate was then redeveloped in developing solution A. The resulting plateis as shown in FIG. 2C. The grained oleophilic aluminium plate has areas1b with no coating thereon. On areas 1c it is coated with the U.V. lightcured fluoro coating 5.

The plate shown in FIG. 2C can be inked up with an oleophilic ink whichadheres to areas 1b of the aluminium plate but not to areas 1c which iscoated with the cured fluoro composition 5. This inked up plate can beused as a water-less printing plate requiring no fount solution.

In FIG. 3A the plate comprising the same aluminium plate as used in FIG.1 was coated with the same positive working coating composition 2 asused in FIG. 1.

The plate of FIG. 3A was then exposed through mask 3 and then developedin developing solution A to remove the light exposed areas of thephotosensitive composition 2 as shown in FIG. 3B.

The developed plate was then coated overall with a Coconut fatty acid.This remained as a very thin layer 7 on the remaining photosensitivecomposition 2 but did not adhere to the uncovered plate 6 as shown inFIG. 3C.

This plate was then coated overall with the fluoro-alkyl coatingcomposition D shown as 5 and air dried at 120° C. for one minute asshown in FIG. 3D. The plate was then subjected to overall light exposureand was re-developed in developing solution A. The resulting plate is asshown in 3E. The grained aluminium plate 1 has areas 1b with no coatingthereon and areas coated with the ink-releasing fluoro-alkyl coating 5.

The plate shown in FIG. 3E can be inked up with an oleophilic ink whichadheres to areas 1b of the aluminium plate but not on areas which arecoated with the cured fluoro-alkyl 5. This inked up plate can be used asa water-less printing plate requiring no fount solution.

In FIG. 4A the plate comprising the same aluminium plate as used in FIG.1 coated on this plate is a negative working coating composition 9 whichcomprised a triarylmethane dye, a condensation product of4-diazodiphenylamine sulphate and formaldehyde (p-toluene sulphonic acidsalt) and an epoxide resin.

Coated on the diazo resin 9 is the same positive working photosensitivecomposition A as used in FIG. 1 this is shown as 2. These coatings areshown in FIG. 4A.

The plate of FIG. 4A is then exposed through mask 3, to expose only theoverlying positive coating, developed in developing solution A, thus theexposed areas of the positive photosensitive layer 2 are removed by thedevelopment step and overall coated with siloxane coating composition Ashown as 5. The siloxane coating is then heat cured at 110° C. for 1minute.

The plate of 4B is then overall light exposed and is redeveloped indeveloping solution A. This yields the plate shown in FIG. 4C. In thisfigure the plate 1 is coated overall with hardened diazo resin 9c. Onthe areas of the plate of FIG. 4C which were exposed in the firstexposure step through the mask 3 is the cured siloxane resin 5. Theareas of the plate not covered by the siloxane resin 5 comprise thephotohardened diazo resin which is especially oleophilic. Thus the plateof FIG. 4C can be inked up and the oleophilic ink adheres extremely wellto the areas 9c not covered with the siloxane and can be used as awater-less lithographic plate.

In FIG. 5A again the same aluminium plate is used. On this plate iscoated a layer 12 of ethyl cellulose. This substance when dried forms anoleophilic layer. Coated on the ethyl cellulose layer 12 is a layer ofpositive working photosensitive resin. These coatings are shown in FIG.5A.

The plate in FIG. 5A is then exposed through mask 3, developed indeveloping solution A and overall coated ink siloxane coatingcomposition A shown as 5 in FIG. 5B. The siloxane coating is then heatcured at 110° C. for 1 minute.

The plate of FIG. 5B is then overall light exposed and is redeveloped indeveloping solution A. This yields the plate shown in 5C. This plate canthen be inked-up with a oleophic ink which adheres only to the ethylcellulose layer 12. The ink does not adhere to the areas of ethylcellulose coated by the silicone coating 5. Thus a water-less printingplate is produced.

Other oleophilic yielding layers can be used in the plate of FIG. 5Ainstead of ethyl cellulose.

After the redevelopment step all the plates prepared with reference toFIGS. 1 to 5 were dried and were then inked using a rubber roller andwater-less plate ink. They were then placed in a printing press and inevery case several thousand good prints were obtained.

What is claimed is:
 1. A method of preparing a water-less lithographicplate comprising:imagewise exposing for a first time a plate having apositive working photosensitive composition on an oleophilic base anddeveloping the plate to remove the areas of the photosensitivecomposition which have been light exposed, coating overall the surfaceof the plate with a layer of a composition which is ink-releasing orwhen cured becomes ink releasing, then either as a separate step or as acombined step curing the ink-releasing composition or drying theink-releasing composition and light exposing overall the plate a secondtime, then redeveloping the plate to remove the photosensitivecomposition remaining after the first development and the ink-releasingcomposition which overlaid the photosensitive composition, herebyproviding a lithographic plate.
 2. A method according to claim 1 whichcomprises the additional step between the developing step and the stepof coating overall the plate with an ink releasing substance of treatingthe plate with an oleophilic coating composition which adheres to theremaining positive working composition but which does not adhere to theexposed base to form an optically light transparent coating having athickness less than the thickness of the positive working composition onthe remaining positive working composition.
 3. A method according toclaim 2 wherein the oleophilic coating composition comprises art esterbased on coconut fatty acid.
 4. A method according to claim 1 whereinthe ink-releasing composition is heat curable.
 5. A method according toclaim 1 wherein the ink-releasing composition is ultraviolet curable. 6.A method according to claim 5 wherein a single exposure to ultravioletlight exposes the photosensitive composition and cures the ink-releasingcomposition.
 7. A method according to claim 1 wherein the ink-releasingcomposition is dried before the plate is re-exposed.
 8. A methodaccording to claim 1 wherein the oleophilic base is an aluminium platewhich has been physically or chemically treated to render it oleophilic.9. A method according to claim 1 wherein the ink-releasing compositionis either a silicone based polymer or a fluoroalkyl compound.
 10. Amethod according to claim 1 wherein the ink-releasing compositioncomprises a water-soluble polymer.
 11. A method according to claim 10wherein the water-soluble polymer is polyvinyl alcohol or hydroxypropylcellulose.
 12. A method according to claim 1 wherein positive workingphotosensitive composition comprises an 0-quinone diazide compound. 13.A method according to claim 1 wherein there is present between the baseplate and the positive working photosensitive composition an oleophiliclayer to which the positive working photosensitive composition canadhere.
 14. A method according to claim 13 wherein the oleophilic layeris a negative working plate.
 15. A method according to claim 13 whereinthe oleophilic layer is a layer of ethyl cellulose.
 16. A methodaccording to claim 1 wherein a curing inhibitor for the ink-releasingcomposition is present in the positive working photosensitive layer. 17.A method according to claim 16 wherein the curing inhibitor ishydroquinone.
 18. A method according to claim 1 wherein the positiveworking photosensitive composition comprises at least one cellulosiccompound.
 19. A method of preparing a water-less lithographic plateby:(a) imagewise exposing a first time a plate having a positive workingphotosensitive composition on an oleophilic base; (b) developing theplate to remove the areas of the photosensitive composition which havebeen light exposed; (c) treating the plate with an oleophilic coatingcomposition which adheres to the remaining positive working compositionbut which does not adhere to the exposed base to form an optically lighttransparent coating having a thickness less than the thickness of thepositive working composition on the remaining positive workingcomposition; (d) coating overall the surface of the plate with a layerof a composition which is ink-releasing or when cured becomesink-releasing; (e) either as a separate step or as a combined stepcuring the ink-releasing composition or drying the ink-releasingcomposition and light exposing overall the plate a second time; and (f)redeveloping the plate to remove the photosensitive compositionremaining after the first development and the ink-releasing compositionwhich overlaid the photosensitive composition.
 20. A method according toclaim 19 wherein the oleophilic coating composition comprises an esterbased on coconut fatty acid.
 21. A method according to claim 19 whereinthe oleophilic base is an aluminum plate which has been physically orchemically treated to render it oleophilic.
 22. A method according toclaim 19 wherein the ink-releasing composition is either asilicone-based polymer or a fluoroalkyl compound.
 23. A method accordingto claim 19 wherein the ink-releasing composition comprises a proportionof a water-soluble polymer which is polyvinyl alcohol or hydroxypropylcellulose.
 24. A method according to claim 19 wherein there is presentbetween the base plate and the positive working photosensitivecomposition an oleophilic layer of ethyl cellulose to which the positiveworking photosensitive composition can adhere.
 25. A method according toclaim 19 wherein the positive working photosensitive compositioncomprises at least one cellulosic compound.
 26. A method of printingusing a water-less lithographic plate comprising:(a) providing alithographic plate obtained by (i) imagewise exposing for a first time aplate having positive working photosensitive composition on anoleophilic base, (ii) developing the plate to remove the areas of thephotosensitive composition which have been light exposed, (iii) coatingoverall the surface of the plate with a layer of a composition which isink-releasing or when cured becomes ink releasing, (iv) either as aseparate step or as a combined step curing the ink-releasing compositionor drying the ink-releasing composition and light exposing overall theplate a second time, and (v) redeveloping the plate to remove thephotosensitive composition remaining after the first development and theink-releasing composition which overlaid the photosensitive composition;(b) inking the plate; and (c) contacting, the plate with a printablemedium.
 27. A method of preparing a water-less lithographic platecomprising:(a) imagewise exposing for a first time a plate having apositive working sensitive composition on an oleophilic base selectedfrom the group consisting of aluminum, plastic and treated paper; (b)developing the plate to remove the areas of the photosensitivecomposition which have been light exposed; (c) coating overall thesurface of the plate with a layer of a composition which isink-releasing or when cured becomes ink releasing; (d) either as aseparate step or as a combined step curing the ink-releasing compositionor drying the ink-releasing composition and light exposing overall theplate a second time; and (e) redeveloping the plate to remove thephotosensitive composition remaining after the first development and theink-releasing composition which overlaid the photosensitive composition,thereby providing a lithographic plate.
 28. A method of printing using awater-less lithographic plate comprising:(a) providing a lithographicplate prepared by (i) imagewise exposing for a first time a plate havinga positive working photosensitive composition on an oleophilic baseselected from the group consisting of aluminum, plastic and treatedpaper, (ii) developing the plate to remove the areas of thephotosensitive composition which have been light exposed, (iii) coatingoverall the surface of the plate with a layer of a composition which isink-releasing or when cured becomes ink releasing, (iv) either as aseparate step or as a combined step curing the ink-releasing compositionor drying the ink-releasing composition and light exposing overall theplate a second time, and (v) redeveloping the plate to remove thephotosensitive composition remaining after the first development and theink-releasing composition which overlaid the photosensitive composition;(b) inking the plate; and (c) contacting the plate with a printablemedium.